两种人工机械心瓣启闭过程的ALE有限元分析

本文采用任意拉格朗日－欧拉（ＡＬＥ）有限单元法，将血液视为不可压缩粘性流体，同时将人工机械瓣简化为定轴转动刚体，建立了机械心瓣／血液耦合运动的二维计算模型．在此基础上．计算了顺向人工机械瓣（ＤＤＭ）的开闭过程，并与Ｓｔ．Ｊｕｄｅ瓣（ＳＪＭ）进行了对比．由本文研究可得以下主要结论：１．ＤＤＭ瓣与ＳＪＭ相比，开启较为迅速，关闭则较为柔和．２．ＤＤＭ瓣的峰值回流量较之ＳＪＭ瓣小．本文研究表明ＤＤＭ瓣由于更好利用了天然心瓣的关闭机理，而具有较高的耐久性潜力．     

人工机械心瓣启闭过程的ALE有限元分析

本文采用任意拉格朗日－欧拉（ＡＬＥ）有限单元法，将血液视为不可压缩粘性流体，同时将人工机械瓣简化为定轴转动刚体，建立了机械心瓣－血液耦合运动二维计算模型，解决了人工机械瓣启闭过程的计算问题．对Ｓｔ．Ｊｕｄｅ瓣启闭过程的数值分析表明：１．Ｓｔ．Ｊｕｄｅ瓣启闭过程包括四个阶段，即：Ⅰ．开启相；Ⅱ．开启保持相；Ⅲ．关闭相；Ⅳ．关闭保持相．２．Ｓｔ．Ｊｕｄｅ瓣关闭时回流明显，伴有显著水击效应．３．在启闭过程中，高剪力区位于两瓣叶间及瓣环附近．本文的研究突破了以非耦合的方法研究心瓣启闭过程的局限性．     

实时三维经食管超声心动图诊断人工机械瓣卡瓣的应用价值

目的探讨实时三维经食管超声心动图（RT-3D-TEE）诊断人工机械瓣卡瓣的临床应用价值。方法回顾性分析10例经手术证实为人工机械瓣卡瓣患者的RT-3D-TEE资料,其中二尖瓣位7例,主动脉瓣位3例。结果机械瓣开放幅度明显减小8例;人工机械瓣呈固定半开放状态2例,瓣口流速增快并有中量反流;见低回声附着于瓣环5例,4例瓣环处见稍高回声赘生物,1例瓣柱结构模糊。手术证实血栓形成6例,肉芽组织增生2例,伴有纤维组织侵入1例,人工机械瓣瓣柱断裂1例。结论RT-3D-TE可对人工机械瓣卡瓣及其原因进行较准确评价。     

三维浮式结构的流固耦合动力特性分析

对于采用位移，压力有限元格式从流固耦合系统导出的大型非对称矩阵特征值问题，构造出了一种新格式的迭代Amoldi方法进行非对称特征值分析来获得浮式结构的动力特性，该迭代格式在克服零频的移频技术中，可以高效地计算出Arnoldi向量，实例分析结果表明，流固耦合作用对水上大型薄壁浮式结构动力特性具有重要影响。     

锥形血管入口区域内管壁与血液的耦合运动

本文研究了锥形血管入口区域内血管壁与血液间的耦合问题。对具有锥度角的弹性血管入口区域内的管壁运动和血液流动建立的相互耦合作用的数学模型，在满足相应的边界条件下求得了一组血液流动的速度分布公式、压力分布公式以及管壁运动公式，得出了一些重要的结论。     

具有结构阻尼的热弹性梁耦合系统的整体解

考虑热效应对弹性梁的影响,研究了一类具有结构阻尼的热弹性梁耦合系统的整体动力行为,采用Galerkin方法证明了该系统整体弱解的存在唯一性.     

不同边界条件对路基结构动力学响应的影响

分别采用静力人工边界、无限元边界、粘弹性动力人工边界和远置静力人工边界对承受交通载荷的典型路基结构进行有限元分析。以远置静力人工边界计算获得的路面竖向位移和面层底部拉应力时程曲线为参考解,揭示边界条件对路基结构动力学响应的影响。分析结果表明:边界条件对拉应力的影响很小,它们与参考解的最大误差为0.82%;静力人工边界下的位移时程曲线一直在参考解附近震荡,无限元边界下的位移解高于参考解,粘弹性动力人工边界下的路面位移与参考解最为接近。综合考虑位移和应力的精确度与CPU的计算时间,粘弹性动力人工边界为最佳的路基结构动力学分析边界条件。     

三维非定常/定常不可压缩流动N-S方程基于人工压缩性方法的数值模拟

基于人工压缩性方法提出一中心与迎风混合的算法，以数值模拟N-S方程的定常／非定常解，对半离散方程的左端采用中心差分，方程右端数值流量采用迎风Roe近似算法，其精度可达三阶．湍流模式利用Baldwin-Lomax代数模式。计算例子包括二维平板、机翼剖面、扁椭球、颅动脉瘤等。计算结果表明，压力和摩擦系数与实验符合，在分离涡旋区计算值与实验有差别，这或许是由于湍流模式不够精确的缘故。     

质量文化传播与工程管理行为耦合演化的系统动力学模型研究

为了研究质量文化建设与工程管理行为以及工程绩效的耦合演化规律,对大型工程中的质量文化建设的动态特性进行了分析,运用系统动力学构建了包括质量文化传播、工作流程、人员调配以及进度压力这四个主要模块相互整合的大型工程耦合演化系统模型。系统仿真的结果表明一些管理行为因忽视了其引发的涟漪效应,导致了质量文化建设和工程建设的失败,而该模型考虑了大型工程存在的返工回路等多种动态反馈,能够帮助工程管理者理解质量文化建设存在的动态复杂性。     

一类耦合梁方程组在非线性边界条件下解的长时间动力行为（英文）

本文研究一类具有强阻尼项的耦合梁方程组在非线性边界条件下的长时间动力行为,首先利用一些常用不等式和先验估计证明该系统存在唯一的整体解,其次通过证明系统存在有界吸收集和半群的渐近光滑性得到整体吸引子的存在性.     

A model of the relay valve used in an air brake system

The mathematical model governing the response of the relay valve in an air brake leads to a hybrid system in which different governing equations apply to different phases of the response of the air brake. To accurately describe the brake’s response characteristics it is imperative to take into account this hybrid structure, and it is to this aspect of the problem that this paper is addressed. The safe operation of any vehicle on the road depends, amongst other things, on a properly operating brake system. Most commercial vehicles such as trucks, tractor–trailers, buses, etc., are equipped with an air brake system. Any defect in a brake system can degrade its performance seriously and can lead to accidents. It is desirable and also important to develop systems that can control and diagnose air brake systems in order to both sustain and improve their performance. One approach to develop such systems is by obtaining a model of the air brake system and then using the same in the design process. The air brake system currently used in commercial vehicles can be broadly divided into a pneumatic subsystem and a mechanical subsystem. One of the main components in the pneumatic subsystem is the relay valve which operates the brakes on the rear axles of a tractor and the axles of a trailer. A relay valve has different modes of operation and the pressure response of the relay valve can be naturally described as the response of a hybrid system. In this article, we develop a hybrid dynamical model to predict the pressure response of the relay valve. An air brake testing facility has been set up at Texas A&M University and this model will be corroborated against experimental data obtained from the same.     

Thermal-fluid-structure coupling analysis for valve plate friction pair of axial piston pump in electrohydrostatic actuator (EHA) of aircraft

This paper deals with thermal-fluid-structure coupling analysis for valve plate friction pair of axial piston pump in electrohydrostatic actuator (EHA) of aircraft. The axial piston pump with high pressure and high rotational speed to be widely applied in EHA of more electric aircraft can increase the power density, but it also deteriorates thermal-fluid-structure coupling of the friction pairs. In order to reveal its interior multiphysics field coupling mechanism, taking the valve plate friction pair in three key friction pairs for example, this study carries out the research on multiphysics field coupling. Firstly, Navier–Stokes equations and energy equation of the incompressible fluid considering the influence of temperature and pressure on the oil properties, heat conduction governing equation with many boundary conditions including heat flux, heat convection, heat radiation and considering the influence of the structure deformation on the temperature and the influence of the temperature on the material properties, the elastic mechanics model of the structure exerted together by temperature, fluid pressure and mechanical load, are established. On this basis, a complete set of fast and effective thermal-fluid-structure coupling method is originally presented, and the numerical analysis is conducted using it for the valve plate friction pair. By the calculation results, the evolution laws with time and space are revealed regarding to the pressure and temperature of the fluid in the chambers, and the temperature, stress and deformation of the valve plate friction pair, the wedge-shaped clearance forms between them, even mixed friction occurs, and the corresponding improving measures aimed at the discovered problems are discussed. These results can provide the theoretical evidence for the design and development of the pump of EHA.     

Collision of incompressible inviscid fluids effluxing from two nozzles

This paper concerns the mathematical theory of the collision problem of two-dimensional incompressible inviscid fluids issuing from two given nozzles. The main result reads that for given two co-axis symmetric semi-infinitely long nozzles with arbitrary variable sections, imposing the incoming mass fluxes in two nozzles, there exists a smooth impinging outgoing jet, such that the two free boundaries of the impinging jet initiate smoothly at the endpoints of the nozzles and approach to some asymptotic direction in downstream, and the pressure on the free surface remains a constant. Furthermore, we show that there exists a unique smooth surface separating the two nonmiscible fluids and there exists a unique stagnation point in the fluid region and its closure. Moreover, some results on the uniqueness and the estimates of the location of the impinging outgoing jet are also established. Finally, the asymptotic behaviors, the precise estimate to the deflection angle and other properties to the impinging outgoing jet are also considered.     

Fluid pressure penetration for advanced FEA of metal-to-metal seals

This numerical study investigates the behaviour of the contact faces in the metal-to-metal seal of a typical pressure relief valve in the commercial FE-package ANSYS. The valve geometry is simplified to an axisymmetric problem, which comprises a simple representative geometry consisting of only three components. A cylindrical nozzle, which has a valve seat on top, contacts with a disk, which is preloaded by a compressed linear spring. Analysis considerations include the effects of the Fluid Pressure Penetration (FPP) across the valve seat which exists at two different scales. In-service observations show that there is certain limited fluid leakage through the valve seat at operational pressures about 90% of the set pressure, which is caused by the fluid penetrating into surface asperities at the microscale. At the macroscale, non-linear FE-analysis using the FPP technique available in ANSYS revealed that there is also a limited amount of fluid penetrating into gap, which is caused primarily by the global plastic deformation of the valve seat. Accurate prediction of the fluid pressure profile over the valve seat is addressed in this study by considering the FPP interaction on both scales. The shape of this pressure profile introduces an additional component of the spring force, which needs to be considered to provide a reliable sealing. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling of aortic valve dynamics in a lumped parameter model of left ventricular-arterial coupling

A lumped parameter model of the sub-system of left ventricle, aortic valve, systemic arteries, systemic capillaries and systemic veins was considered during systole. A model of aortic valve dynamics based solely on geometrical and kinematical consideration is defined. The model is described by two geometrical parameters of aortic valve and a few kinematical relationships. The proposed model mimics the incisures in the aortic flow and aortic pressure very well. We showed that the dicrotic notch could be explained by aortic valve closing in terms of a lumped parameter model, without a need for any wave reflection theory. According to the proposed model the effects of aortic valve dynamics on the aortic flow and pressure are mainly limited to the valve opening and closing periods. The model offers a new paradigm for defining a more realistic left ventricle model.      

Modelling of a Switching Control Hydraulic System

Modelling of a hydraulic system featuring a specific type of switching control is presented. Despite conventional hydraulic drive technology where rather smooth changes of pressure and flow rate are intended and where oscillations constitute undesired phenomena, switching control provokes oscillations as an indispensable element to achieve high energetic efficiency with valve control. The system under study is one which comprises a novel switching valve, a long line with considerable wave propagation dynamics, a hydraulic cylinder, and the valve's dynamics.     

Modeling and numerical simulation of fluid flow induced by the sutureless 3F-Enable aortic valve

Diseases of the aortic valve belong to the most common health problems. The aortic valve maintains the blood flow in one direction and serves to prevent retrograde flow from aorta to the left ventricle. To date, new bio-prosthetic, suturless heart valves have been designed. The purpose of the present study is therefore to evaluate their influence on hemodynamics in the cardiovascular system. Especially the blood flow in the vicinity of the aortic valve, in the sinus of Valsalva and the ascending aorta becomes on importance from the fluid dynamical point of view. The three-dimensional geometrical model is generated after segmentation of CT data of the 3F-Enable aortic valve prosthesis. A set of simulations with different initial velocity profiles and pulse frequencies has been created to examine the transient behavior of the fluid flow and the heart valve prosthesis. The function of heart valve system, however, involves an analysis of fluid-structure interaction to predict the motion of leaflets. Hence, the separation of the soft tissue and the hard nitinol-based frame is carried out. The results reveal pressure and velocity distributions as well as normal and shear stresses acting on the wall of the prosthesis and aorta. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The ANN application in FEM modeling of mechanical properties of Al–Si alloy

Artificial neural network (ANN) is a nonlinear dynamic computational system suitable for simulations which are hard to be described by physical models where, rather than relying on a number of predetermined assumptions, data is used to form the model. In order to predict the mechanical properties of A356 including yield stress, ultimate tensile strength and elongation percentage, a relatively new approach that uses artificial neural network and finite element technique is presented which combines mechanical properties data in the form of experimental and simulated solidification conditions. It was observed that predictions of this study are consistent with experimental measurements for A356 alloy. The results of this research were also used for solidification codes of SUT CAST software.     

Modeling and simulation of thermal chlorine etching of gallium arsenide with application to real-time feedback control

A dynamic model for the simulation of thermal chlorine etching of gallium arsenide is developed. The primary motivation for the development of the simulation is the design and testing of real time adaptive feedback controllers which rely upon in-situ optical measurements of etch depth obtained via spectroscopic ellipsometry. The basis for the model is an empirically derived relationship between etch rate, chlorine pressure, and substrate temperature. The chlorine pressure in the chamber is regulated by a throttle valve which determines the effective pumping rate of a turbo-molecular pump which is used to evacuate chlorine pressure dynamics and a second-order damped harmonic oscillator with zero-order hold valve position command inputs is used to model the dynamics of the throttle valve. An output equation is used to model the fact that ellipsometry based etch depth and chamber pressure can be observed at discrete time intervals. Unmeasurable parameters which appear in the model are identified, and the model is validated using experimental data. An adaptive linear-quadratic Gaussian based controller based on our model which forces etching to precede at a desired rate while estimating the often difficult to measure substrate temperature is designed and then tested using our simulation.